Cryopreservation and cryoprocessing of mediums such as biopharmeceuticals and foods are important in the manufacturing, use, and sale of these products. However, in order to process many of these products, the cryopreservation or cryoprocessing must be done uniformly and in a controlled manner or the value of the product may be lost. For example, when processing cells for cryopreservation, if the cells are frozen too quickly with too high of a water content, then the cells will rupture and become unviable.
Uniformity can be achieved using small containers in which the volume of the medium in the container is small enough to allow it to be uniformly cooled. However, such small containers only allow small quantities of a product to be processed at one time, and thus are of limited commercial value. Additionally, as the size of the container is increased, the processing speed must be reduced in order to maintain uniformity in the processing.
One technique which has been used to cryoprocess foods in larger quantities is a system which mixes the product as it is frozen. Using traditional refrigerators or freezers during this process would take too long since the heat is extracted from the medium too slowly. Therefore, commercial systems have operated by spraying carbon dioxide snow on the product while it is mixed in order to rapidly cool it. Carbon dioxide snow, however, is a solid and therefore often makes less thermally conductive contact with solids in the medium and will not usually cool them quickly. This is beneficial for products which can be denatured if they are cooled too rapidly.
Liquid nitrogen is colder than carbon dioxide snow and can more quickly extract heat from a medium or product. Some commercial cryoprocessing systems have operated by spraying liquid nitrogen on the product or mixing the product with a liquid nitrogen mist. This allows for very rapid processing of a product and makes liquid nitrogen very useful in commercial cryoprocessing. Liquid nitrogen, however, may cool a product too quickly and can damage or destroy the usefulness of the product by, for example, denaturing it.
What is needed is a system and a method for cryoprocessing or cryopreservation of a medium or product which can make use of the properties of carbon dioxide snow and liquid nitrogen for cryoprocessing or cryopreservation of a medium or product without destroying its commercial utility.